Early morning traffic makes its way along the 91 Freeway in Riverside County. A new report from a nonpartisan think tank finds that the recently passed $52.4 billion transportation funding bill, which raises the gas tax by 12 cents a gallon, isn’t a long-term solution for California’s transportation needs. (File)

A newly passed transportation funding bill that raises California’s gasoline tax by 12 cents a gallon isn’t a long-term fix for the state’s crumbling roads, according to a report released Monday by a nonprofit, nonpartisan think tank.

Better fuel economy and the growing number of electric, hybrid and zero-emission vehicles make the gas tax an outmoded, unreliable funding source for transportation, states the report, “Beyond the Gas Tax: Funding California Transportation in the 21st Century,” put out by Next 10 in conjunction with Beacon Economics.

That’s despite the tax increases called for in the transportation bill, SB 1.

“SB 1 may prove to be a temporary solution to a growing and permanent problem,” Adam Fowler of Beacon Economics said in a news release.

The Legislature passed SB 1, or the Road Repair and Accountability Act of 2017, in early April. SB 1 would raise $52.4 billion over 10 years for road repairs and other transportation projects by increasing the gas tax, which would be adjusted annually for inflation.

Prior to SB 1, the state’s gas excise tax had not been raised in roughly 20 years. SB 1’s backers said inflation has eroded the tax’s ability to fix roads.

SB 1 also raises diesel taxes and imposes new annual fees on vehicles. Gov. Jerry Brown, who championed the bill, is expected to sign it soon.

In a telephone interview, SB 1’s author, state Sen. Jim Beall, D-San Jose, said the bill “is designed to reduce the one-time cost of the road repair backlog at the state and local level.”

“It’s kind of like your mortgage,” he said. “Once you pay it off, your costs are lower.”

Chris Lee, a legislative analyst with the California State Association of Counties, said SB 1 is meant to be a bridge to a long-term funding system to maintain California’s roads. In the meantime, it addresses the road repair backlog that’s built up now.

Through the new annual fees on vehicles, SB 1 will raise money for transportation in a way that’s not linked to fuel prices, he added.

While calling SB 1 a good start, $52.4 billion “falls short of current $137 billion deferred maintenance deficit that has not been addressed,” Next 10 said.

That deficit may continue to grow, the group said.

“Inflation adjusted fuel-tax revenue declined 20 percent from 2010 to 2015, despite the fact that Californians have been driving more every year, logging a record 335 billion vehicle-miles traveled